With excellent properties and easy melt molding, polyamides are broadly applied to materials for clothes, fibers for industrial materials, engineering plastics, and the like. However, general polyamides have problems of insufficient heat resistance, low dimensional stability caused by absorption, and the like. Recently, polyamides used in the field of electric/electronic components, car components, and the like are required to have further improved properties and functions. Particularly, there is a need for development of polyamides that have further improved properties in terms of high thermal resistance, dimensional stability, mechanical properties, chemical resistance, treatment in polymerization or molding, and the like.
In a polyamide production method known in the art, polyamides are produced through polycondensation by heating a salt or a low-order condensate formed of typical dicarboxylic acid and diamine under melting conditions. Such a production method can be applied to a method for producing polyamides using p-xylylenediamine as a diamine component. For example, a method for producing polyamides from p-xylylenediamine, m-xylylenediamine, and aliphatic dicarboxylic acid (see JP Patent Publication No. S32-06148, JP Patent Publication No. S44-20637, and JP Patent Publication No. S47-15106), a method for preparing polyamides from p-xylylenediamine, hexamethylenediamine, adipic acid and terephthalic acid (see JP Patent Publication No. S47-33277), etc. In addition, JP Patent Laid-open Publication No. H08-03312 discloses a method for producing polyamides having a structure derived from xylylenediamine and benzene dicarboxylic acid through multistage melt polymerization using a plurality of polymerizing devices.
However, when applied to preparation of polyamides having a high melting point, the above methods can cause pyrolysis of reaction products due to high temperature conditions for maintaining a molten state and the polyamides prepared by the methods are likely to suffer from property deterioration in terms of mechanical strength, heat resistance, color, and the like. Moreover, the polyamides prepared by the above methods have high viscosity and are difficult to treat due to gel content thereof, and are likely to remain on an inner wall of a reactor, thereby causing reduction in yield.